Running power to my first shop - triplex or quadruplex?

After multiple forum posts on the issue, then settling, then getting new information on it, I’m once again dumbfounded on how to run power to my shop.

Quickfire stats: Running ~70ft cable direct buried from 200A panel to 100A subpanel in a detached shop (300sqft). No pipes/wires in between the two structures. Using #2 Aluminum, so putting in a 90A (or 100A?) breaker in the panel back up at the house. Interior shop wiring features multiple 120V and 240V circuits. I’m quite future proofed and have wired for the following: dedicated circuit for dust collection, dedicated circuit for air compressor, multiple outlets pigtailed and dotted around just in case – tools hooked up to these would never be used at the same time.

So the question: 2-2-4 aluminum, or 2-2-2-4?

I believe I understand that quadplex is the ‘correct’ way, but this work is not being inspected. I want it to work, and don’t want to kill myself and/or others, but I really need some pragmatic advice here – not just “do it by the code” – because my electrician says 2-2-4 will suffice. I need to know if he’s saying that because he’s been there done that and it’s good enough, or because he’s a cowboy who wants to use what Home Depot sell 20 minutes away.

Thanks all

53 replies so far

It sounds like you know what the code indicates. But I’ll tell, I live in an incorporated area (no inspection) and my electric provider (a co-op) told to run the 2-2-4. Then, when we moved 5 years ago, I had the current shop wired by local electricians (both shops were a 100 amp sub panel). He ran 2-2-4 to it. This was also approved (again, no inspection….they just happened to be here during the work) but the provider, this tine it was the village I live near that has municipal power. You won’t kill your self, and it works just fine.

Hire a licensed electrician! If you screw up the install in any way a fire might destroy everything and you will have to deal with your insurance company. Hiring a licensed and experienced electrician will cost a little bit more but if anything goes wrong, you and your insurance company can go after the company you hired.

+1 on licensed electricianIf you do it yourself you only need triplex wire, quadplex is for 3 phase power. If you don’t have any tools that require 3 phase power triplex should work fine. one thing be sure to bury it deep enough and make sure backfill has no sharp rocks in it. 70 foot run to your shop is not that far, if it was me i would put it in plastic conduit. no power leaks to earth ground and insulation on wire will last, the covering on the wire is not very thick. I learned this from exp. cost me way more in power draining to ground and had to replace it all. good luck

I would definitely run it in plastic conduit. While you at it, you might want to run another conduit with wire for low voltage light switch,phone, intercom or cable. I know all this stuff is going wireless, but it’s difficult to predict what you might want/need in the future. You could even use plastic water line. My concrete contractor thought I was a pain with all the plastic nipples and under concrete conduit, but I ended up using every one. Put the line/rope in while you lay it, and pull another line anytime you that one through. That will eliminate fishing.Dan Coleman

But you already know the answer. You mentioned it yourself in the original post. And it has nothing to do with 3-phase. Now let’s talk why…

In the US, 220V power is actually 2 X 110V legs 180 degrees out of phase. 220V loads do not cause any currents in the Neutral leg. As a matter of fact, equivalent loads on both 110V legs will not cause current in the neutral line since the neutral currents from both legs are out of phase and cancel. But, if the full capacity of the feeder is used on only 1 X 110V leg, then the neutral line must be able to carry the entire return current and should be the same size.

There are also grounding issues. This is a feeder to a subpanel in a detached building and NEC requires a separate ground run from the main panel and isolated ground and neutral at the subpanel in the detached structure. In addition, they require ground stakes at the subpanel. NEC will (or did, I am not sure about the latest NEC rev) allow the ground wire to be smaller than the feeders. The goal here is to keep only one connection between GND and neutral at the main panel. The separate ground run back to the main panel is to cover situations where the neutral may become disconnected and prevent a return path through ground (real ground as in dirt).

So you really want 2-2-2-4 with red, black and white connected to 2 and green connected to 4.

I wired my attached 2 car garage… for it was simple. But a detached building? Yep, I would go licensed electrician for sure. The depth of the conduit, HOW it raises out of the ground, HOW it penetrates thru the wall, bleh bleh bleh. Also, if you get it inspected and call it a “subpanel”, get ready for a scowl :) I was told (by NV inspector) it’s not a subpanel but… something else (forget). If I would of written “subpanel” on the initial plans for the permit, they would of said no to the whole thing.

-- Yes, my profile picture is of a Carpenter Bee! The name is derived from the Ancient Greek "wood-cutter"

Just because it works doesn’t make it right. I have heard that placing a separate ground rod at the sub panel is being accepted I don’t know from my own experience though. I do know that they have gotten very stringent on how the ground is installed though and in some cases it is required to be set in the foundation of the building. dryers and stoves now are required to be wired with four leads regardless if the appliance splits the 220 internally for 110. A ground is required to be a separate conductor until joined in the main panel. The ground cannot be used as a current carrying conductor and is meant for safety only. Of course it will work that way, but the safety of the system is reduced. If the neutral for some reason is interrupted, bad connection causing high resistance for instance, someone touching the equipment can become the path of least resistance. Of course this could happen in turn with the ground as well but you have more than doubly reduced the possibility. I have seen the way some people stuff the wires into the wire nuts using a yellow instead of a red because it is in their hand. long and short the extra wire is not that much additional expense for the additional safety.

No to aluminum.Yes to 2-2-4.Also pay attention to the Christmas tree rule – in other words, the top of the tree is the smallest and final breaker. So you put a 100 amp breaker in the main box coming into your sub-panel, and run maybe an 80 amp breaker in your sub panel as a main.That way, you blow the sub before you overload the main panel back at the house. Always done it this way in four of five shops I’ve owned as I moved around – always kept me safe. Also, run some extra ground bars into the ground with the sub – usually two at least eight feet apart outside. Use both a neutral bar AND a ground bar in your sub. Be safe not sorry.

I’m going with an electrician (a different one than who insisted on 2-2-4).

This electrician is well known and trusted in the area and uses 2-2-2-4, but the only thing throwing me off is the whole issue of floating the ground and running it back to the main panel. This is instead of grounding at the subpanel, and is done to avoid feedback and all that stuff.

It makes sense to me, but my reading has led me to believe that code requires grounding rods.. Now, I’m not doing it strict to code, but I still want it safe. Can anyone explain to me floating vs grounding rods?

That is an interesting contradiction. You only get one of those two options; by code and safe or scabbed in any old way that feels good at the time (I guess).

The National Electric Code requires 4 conductors for 120/240 single phase: 2 hot, 1 neutral (current carrying grounded conductor) and the equipment ground. You also need ground rods at the subpanel that connect to the equipment ground. The equipment ground and the neutral are separate once they leave the main service where they are bonded together. I asume that is what you mean by “floating ground”. You also need a main disconnect in the detached building that kills everything with a single switch. It will probably be in the subpanel.

There has been a lot of work done testing grounding systems in the last few decades. The “book” on grounding has literally been written. There were many eye opening discoveries that no one had ever dreamed of. It was optional to drive ground rods or run a equipment ground conductor to a detached subpanel 30 years ago. It would have been legal to use the 3 wire option in those days, but not anymore. The current code requires both the equipment grounding conductor and driven rods at the detached location. The code is constantly changing. There have been lots of major changes in the last few updates, every three years, including a total revision. There are lots more coming with the 2014 edition probably adopted about July 1 of this year in most locations. I’m glad I retired before I had to worry about this new code ;-)

I really feel sorry for the public trying to get the truth about electrical work. Here in WA, there is a strict licensing law and enforcement. Yet, there are still handymen and illegal contractors doing dangerous things that border on arson.

BTW, welcome to LJ!

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

Nope! Let’s get this part straight at least – there are no floating grounds! That is dangerous for a number of reasons.

In a three wire feed to a detached building, you run two hots and neutral out to a subpanel. The subpanel then requires a ground stake connected to equipment ground and neutral is bonded to that ground at the subpanel. Be aware that this no longer allowed by the NEC.

In a four wire feed to a detached building, two hots, a neutral and a ground are all run to the detached building. In this case, neutral is not bonded to ground at the subpanel. Ground stakes used to be optional in this situation, now they are required by NEC. I assume this is what you mean by “floating ground”. But it is still connected to a good solid earth ground back at the main panel.

Now, how do I know this? I recently rewired my detached garage and installed a subpanel. I ran a three wire feed initially but wondered why there were two separate bonding connections in the subpanel I bought. After researching the NEC, I had to pull the fourth wire (ground) and make sure that neutral and ground were separated at the subpanel. When I had it inspected, the inspector looked specifically for this and told me it would not have passed without 4-wire feed.

Google it! I did. You’ll find enough horror stories to convince that this is the right way to wire things. Problems come up when any one of the feed wires might open. In the case of three wire feed if the neutral opens, fault current might return through real ground (dirt!), In this case there might be enough limit to current that main breakers would never trip under faults. In the case of four-wire feed, the ground connection back to main panel might open leaving the grounds at the subpanel truly floating and this is dangerous. Thus the newer requirements for ground stakes at the subpanel with four-wire feed.

I’m definitely now using 4 wire (2-2-2-4) and will have a licensed electrician make the connections.

I think my incorrect use of contractor spiel has led to some confusion. I apologize, as you’ve all put a lot of much appreciated effort into your responses.

I’m running 4 wires to this subpanel, and now need to know how to ground it. Do I:1) Bond neutral and ground together on the same grounding bar in the subpanel. If so, where does it go from there? This doesn’t seem correct to me as I’m running 4 wires but this would only give me 3 connections.. 2 hots are sorted, but then I’ve got a neutral and a ground going to the same grounding bar, in that case I may as well use 3 wire feeder, but that’s not correct so…2) Keep neutral and ground on separate bars. The ground hooks up to the ground on my 4 wire feeder, and is run solely back to the main panel to be grounded.3) Keep neutral and ground on separate bars. The ground runs to grounding rod(s) located at the subpanel. In this scenario are they also grounded at the main panel, or is the subpanel ground kept separate from main panel ground?

Good thing you are having a licensed electrician. He should know know do do this properly.

4 wires are required. The neutral and equipment ground are separate after they leave the main panel.

The sub panel grounding bar and neutral bar will be separate in the sub. The panel will come with a “bonding screw” to bond the neutral to the panel enclosure. Do not install it. There are brands of panels that will have the bonding in place from the factory. If yours does, remove it. It should be identified with a green marking screw.

The new ground rods connect to the grounding bar, not the neutral. They are totally separated. At the main panel, the grounds and neutral all go to the same bar and have a bonding to the panel enclosure. This is at the main panel only. If you have 5 sub panels in detached structures, the ground will be separate in each and they all require the additional ground rods.

The ground runs to grounding rod(s) located at the subpanel. In this scenario are they also grounded at the main panel, or is the subpanel ground kept separate from main panel ground? The 4th wire you pull from the main to the sub is the ground conductor. It connects the main panel neutral and to the sub panel ground bar. The ground rods also run to the sub panel ground bar. There should be existing ground rod or rods (depending on the age of the installation) at the main panel.

All your branch circuit grounds go to the grounding bar and all a the neutrals go to the neutral bar. I have seen the branch circuit grounds and neutrals intermingled in a properly installed sub panel.

Grounding is the most confusing issue in the code. The are more corrections written for it than any other article. In the last 45 years, I have had an occasional inspector write a correction for a properly grounded installation ;-)) I have had an electrical engineer specifying a total service rebuild rather than put in a small control transformer because he did not think the new transformer would work because of grounding issues. If he had been correct, the entire power gird and distribution system in this country would not function! Do not feel bad about the confusion. Even inspectors do not agree on the proper grounding for some installations. On one job, the power company and state inspector could not agree on the proper installation! I only relate this to point out how confusing the issue can be for professional, let alone the layman.

The latest requirement for grounding is to use a ufer ground instead of ground rods for new structures. That is connecting to the rebar in the footing instead of using ground rods. Here is WA, if you do not get this done and inspected at the time of the footing pour, you have to wrap the building with a few laps of copper wire to satisfy the grounding requirements. Hopefully, ground rods will suffice for you.

I will make a comment on the brand of panel. Square D and Cutler Hammer are the only 2 brands I would install. If the customer wanted another brand, they needed to find another electrician. Most brands of 15 and 20 amp breakers will hold a dead short long enough to melt a wire the size of a paper clip. Square D and Cutler Hammer have both thermal and magnetic trip. They will save the paper clip. A dead short caught by them will usually not leave a burn mark in a metal enclosure. Most of the others will leave very noticeable burn marks with a little copper contamination to boot.

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence